Patient Basics: Coma and Persistent Vegetative State

Originally published by Harvard Health.

What Is It?

Coma is a deep and prolonged state of unconsciousness resulting from disease, injury or poisoning. The word coma usually refers to the state in which a person appears to be asleep but cannot be awakened.

Persistent vegetative state refers to another form of altered consciousness in which the person appears to be awake but does not respond meaningfully to the outside world. In this condition, the person’s eyes may be open and there may be some yawning, grunting or other vocalizations. In both cases, the patient is alive, but the brain does not function fully.

Some causes of coma include:

  • Head trauma, such as may be sustained in a car accident, sports injury or falling injury
  • Complication of an underlying disease, such as seizure disorder, diabetes or liver or kidney failure
  • Poisoning, usually involving an overdose of drugs that depress the nervous system, such as narcotics, tranquilizers or alcohol
  • Stroke

Coma rarely lasts more than a month and usually ends sooner. Coma may worsen to become a persistent vegetative state.


A person in a coma will be unconscious and unable to communicate. He or she will not respond to light, sound or pain. The person may stretch his or her arms and legs in unusual ways, but the person will not display purposeful movement. In a deep coma, the areas of the brain that control breathing may be affected, and the person may need to be kept alive by an artificial respirator (a mechanical breathing machine).

A person in a persistent vegetative state will be able to breathe without assistance. He or she will have cycles of being awake and asleep. During the awake cycles, the person may react to physical pain and may move, but the movement will not be purposeful.


Coma is usually a straightforward diagnosis because the signs of unconsciousness and unresponsiveness are clear. The cause of the coma can be more difficult to determine.

When coma results from traumatic head injury, the cause usually is clear. Other clues to the cause of coma may be available from the people who called for help. For example, observers can tell health care professionals whether the person took a lot of medication, what symptoms occurred immediately before the coma, and how quickly the person lost consciousness. Doctors also will want to know about the patient’s medical history, because some disorders can lead to coma, including diabetes, seizure disorder and heart, lung, liver, kidney or other disease. A physical examination can give other clues. For example, a narcotic overdose causes very small (pinpoint) pupils that do not react to bright light.

Specific tests that may be used to diagnose coma include:

  • Blood and urine tests to check for disease, metabolic disorders or toxins
  • Magnetic resonance imaging or computed tomography scans to look for bleeding in the brain, tumors, infection or stroke from decreased blood flow
  • Electroencephalogram (EEG), a graph of the electrical output of the brain, which may indicate a metabolic imbalance or persistent seizure activity. An EEG can also be helpful to determine whether there is any electrical activity in the brain.  If there is no electrical activity on repeated EEGs and no reversible cause is found, the patient is brain dead and treatment is futile.
  • Lumbar puncture (spinal tap) to examine the cerebrospinal fluid for signs of meningitis and encephalitis

Expected Duration

How long a coma lasts depends on the cause, location, extent and severity of the damage to the brain. Coma can last hours or many months and can end with recovery, persistent vegetative state or death. Some people who recover from a coma will have permanent physical and psychological disabilities. Some face years of rehabilitation, and others recover fully relatively quickly.


Although coma sometimes cannot be prevented, many cases can be prevented by using safety precautions. For example, many cases of head trauma can be prevented if more people drive safely, wear seat belts when riding in an automobile, and wear helmets when riding on a motorcycle or bicycle. Also, do not drive when drinking alcohol or taking sedating drugs. People with diabetes need to monitor their blood sugar levels often to avoid hypoglycemia. Many medications interact to decrease levels of consciousness, especially when mixed with any alcohol.


Treatment starts with reducing further damage to the brain. Physicians must clear the patient’s airways so he or she is able to breathe. In some cases, the person will have to be put on a mechanical ventilator (breathing machine).

Specific treatment will depend on the cause of the coma. For example, if the coma was caused by head trauma, efforts will be made to stop any bleeding or swelling in the brain. If the coma was caused by a disease, physicians will try to reverse it by treating the underlying condition. If poisoning caused the coma, physicians may give medications to counteract the depressive effects of the substance that caused the coma.

Once the person is treated appropriately for the immediate cause of coma, treatment will focus on supportive care. This usually includes making sure the person does not suffocate, making sure the person’s muscles and ligaments stay flexible, providing adequate nutrition, and taking precautions to help prevent infections, such as pneumonia. Because a person in a coma cannot move on his or her own, it’s important that his or her body be rotated periodically to prevent bedsores.

When To Call a Professional

Seek emergency care if a person appears to be unconscious, is unable to respond or cannot be awakened from a sleep.


Some people make a full recovery, others recover with some remaining physical or intellectual effects and others die of their injuries or condition. It is not always possible to predict who will recover and who will not.

Recovery from a coma is more likely when the cause is identified quickly and the problem that caused the coma is reversed. A person brought to the emergency room with a coma caused by very low blood sugar or a drug overdose has a better prognosis than someone with severe head trauma.

Comas rarely last longer than four weeks. The speed of recovery from a coma can vary a lot. In general, the longer the coma, the less likely the person is to recover.

People in a persistent vegetative state rarely recover.

Additional Info

National Institute of Neurological Disorders and Stroke
P.O. Box 5801
Bethesda, MD 20824
Phone: 301-496-5751
Toll-Free: 1-800-352-9424
TTY: 301-468-5981

American Academy of Neurology (AAN)
1080 Montreal Ave.
St. Paul, MN 55116
Phone: 651-695-2717
Toll-Free: 1-800-879-1960
Fax: 651-695-2791

Brain Injury Association of America
8201 Greensboro Drive
Suite 611
McLean, VA 22102
Phone: 703-761-0750
Toll-Free: 1-800-444-6443
Fax: 703-761-0755